JP5279031B2 - FM demodulator and command receiver using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FM demodulator which can remove or reduce leakage from a demodulation signal component of an adjacent channel to a main signal component. <P>SOLUTION: The FM demodulator includes: demodulation means (12 to 14) which demodulate an adjacent channel together with a desired main channel in a case of demodulation; a digital filter processing means (15) which removes a signal of a desired channel band for a signal after phase detection using a digital signal processing technology in a case that a demodulation signal component of the adjacent channel leaks to the main signal component after demodulation by the demodulation means; a delay circuit (16) which generates the same processing delay time to the digital filter processing means; a composition means (17) which composes the output signal of the digital filter processing means and a signal subjected to delay processing by the delay circuit in an inverse phase; and a differentiator (18) which takes out a frequency modulation component from the signal composed by the composition means. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an FM demodulator and a command receiver using the FM demodulator, and more particularly to a band selection digital processing type FM (Frequency Modulation) demodulator.

  Recently, in satellite command receivers, satellite arrangements in geostationary orbit are adjacent to each other. When a command is transmitted to the target satellite, it becomes an interference wave for the adjacent satellite, and communication between adjacent satellites is not possible. It becomes an obstacle.

  On the other hand, communication with an adjacent satellite becomes a disturbing wave for communication with the target satellite, which hinders communication. There is an increasing demand from customers for command receivers that are not affected by this adjacent channel.

  In the command receiver related to the present invention, the analog signal processing unit in the previous stage of the FM demodulation takes measures by band limitation by the analog type narrow band filter, but from the general performance of the command receiver and the feasibility of the filter The performance against jamming waves cannot meet customer requirements.

  A configuration example of a digital processing type FM demodulator related to the present invention is shown in FIG. In FIG. 2, a digital processing type FM demodulator related to the present invention includes an A / D (analog / digital) converter 11, a bandpass filter 12, a carrier signal generator 13, a phase comparator 14, And a differentiator (frequency detection) 18.

  The above FM demodulator outputs a main channel component obtained by extracting the input FM modulated wave by the bandpass filter 12 and a signal having a frequency substantially the same as the carrier frequency of the modulated wave output from the carrier signal generator 13. Then, after phase comparison is performed by the phase comparator 14 and a phase detection signal is extracted, a frequency modulation component is extracted by a differentiator 18 at the subsequent stage and output as a demodulated signal.

  As the above-described command receiver for mounting on a satellite, there are command receivers described in Patent Documents 1 and 2 below.

JP-A-6-326639 JP-A-8-288897

  In the FM demodulator described above, when outputting as a demodulated signal, a band pass filter for suppressing the adjacent channel component is connected to the preceding stage of the FM demodulator in order to prevent the demodulated signal of the adjacent channel from leaking to the main channel demodulated signal. By doing so, adjacent channel components included in the modulated wave before FM demodulation are suppressed, and leakage to the main channel during demodulation is reduced. The same processing is performed in the command receivers described in Patent Documents 1 and 2 above.

  This bandpass filter is required to have narrowband characteristics and steep out-of-band attenuation characteristics, but since computation by multi-bit quantization is required, due to restrictions on computation processing time in the real time of the signal processor, The bit length is limited, the required characteristics cannot be obtained, the attenuation amount of the adjacent channel component becomes small, and the reduction of leakage is insufficient.

  Accordingly, an object of the present invention is to provide an FM demodulator capable of eliminating the above-described problems and eliminating or reducing leakage of a demodulated signal component of an adjacent channel to a main signal component, and a command receiver using the FM demodulator. It is in.

An FM demodulator according to the present invention is an FM demodulator that performs demodulation by digital processing of an FM (Frequency Modulation) modulated wave,
Demodulating means for demodulating the adjacent main channel together with a desired main channel at the time of demodulation, and when the demodulated signal component of the adjacent channel leaks into the main signal component demodulated by the demodulating means. Digital filter processing means for removing a signal in a desired channel band from the signal after phase detection, a delay unit for generating the same processing delay time as the digital filter processing means, and an output signal of the digital filter processing means, A synthesizing unit that synthesizes the signal subjected to the delay process by the delay unit in reverse phase; and a differentiator that extracts a frequency modulation component from the signal synthesized by the synthesizing unit.

  A command receiver according to the present invention includes the FM demodulator described above.

  According to the present invention having the above-described configuration and operation, it is possible to eliminate or reduce the leakage of the demodulated signal component of the adjacent channel to the main signal component.

It is a block diagram which shows the structural example of the FM demodulator by embodiment of this invention. It is a block diagram which shows the structural example of the digital processing type FM demodulator relevant to this invention.

  Next, embodiments of the present invention will be described with reference to the drawings. First, an outline of an FM (Frequency Modulation) demodulator according to the present invention will be described.

  The FM demodulator according to the present invention demodulates an adjacent channel together with a desired main channel when demodulating the FM modulated wave in digital processing, and the demodulated signal component of the adjacent channel leaks to the demodulated main signal component. In the digital signal processing technique, the digital filter processing for removing the signal of the desired channel band with respect to the signal after phase detection and the signal subjected to the delay processing by the delay device are synthesized in reverse phase, It is characterized in that leakage of the demodulated signal component of the adjacent channel to the main signal component is eliminated or reduced when the frequency modulation component is output thereafter.

  The FM demodulator according to the present invention is an FIR (Finite Impulse Response) type high-pass filter (or band rejection filter) for the phase detection signal output from the phase comparator in the digital processing type FM demodulator related to the present invention. By adding a digital filter process composed of a delay unit, adjacent channel components are removed or reduced, and then FM demodulation by a differentiator is performed.

  FIG. 1 is a block diagram showing a configuration example of an FM demodulator according to an embodiment of the present invention. In FIG. 1, an FM demodulator according to an embodiment of the present invention is an FM demodulator of band selection digital processing type, and includes an A / D (analog / digital) converter 11, a bandpass filter 12, and a carrier signal generation. And a phase comparator 14, a FIR (Finite Impulse Response) type high-pass filter (or band rejection filter) 15, a delay unit 16, a synthesizer 17, and a differentiator (frequency detection) 18. ing.

  In the FM demodulator according to the embodiment of the present invention, the phase modulation component extracted by the phase comparator 14 is branched into two from the FM modulated wave that has passed through the bandpass filter 12 and the output signal of the carrier wave signal generator 13. One is input to the FIR type high pass filter 15, and the other is input to the delay unit 16 that generates the same processing delay time as the FIR type high pass filter 15.

  This FIR type high-pass filter 15 has a characteristic of attenuating only a desired channel component, and has a function of outputting main channel out-of-band frequency components such as adjacent channels without attenuation. Further, in the present embodiment, since the group delay characteristic is made constant by adopting the FIR type high-pass filter 15, phase rotation due to the cutoff frequency does not occur.

  On the other hand, the delay device 16 has a function of delaying for a specified time without attenuation. In the present embodiment, the signal that has been filtered by the FIR type high-pass filter 15 and the inverted signal of the signal that has passed through the delay unit 16 are synthesized by the synthesizer 17 so that the signals cancel each other. Only the desired channel components can be extracted.

  Since the digital filter characteristics under the restriction of the computation processing time in the real time of the signal processor cannot sufficiently attenuate the main channel component, the main channel component is also attenuated in the signal synthesized by the synthesizer 17. However, the adjacent channel component can be sufficiently removed or reduced without having a steep out-of-band attenuation characteristic.

  In this embodiment, it is possible to obtain an FM demodulated signal in which the leakage of the adjacent channel is eliminated or reduced by extracting the frequency modulation component from the signal synthesized by the synthesizer 17 by the differentiator 18 in the subsequent stage. It becomes.

  Thus, in this embodiment, it is possible to separate from adjacent channels. That is, in the present embodiment, the adjacent channel component having an amplitude larger than that of the main channel can be removed by calculation for digital signal processing of the quantized time sample signal. In addition, the removal performance is stable without depending on environmental conditions such as temperature.

  Furthermore, in this embodiment, disturbance signals including noise components outside the main channel can be removed. That is, in this embodiment, signal components including noise signals outside the main channel band including adjacent channels can be removed, and disturbance to the main channel can be removed.

  The present invention can be applied to a demodulator in communication using FM modulated waves in addition to a command receiver mounted on a satellite.

11 A / D converter 12 Band pass filter 13 Carrier signal generator 14 Phase comparator 15 FIR type high pass filter (or band rejection filter)
16 Delay device 17 Synthesizer 18 Differentiator (frequency detection)

Claims (4)

An FM demodulator that performs demodulation by digital processing of an FM (Frequency Modulation) modulated wave,
Demodulating means for demodulating the adjacent main channel together with a desired main channel at the time of demodulation, and when the demodulated signal component of the adjacent channel leaks into the main signal component demodulated by the demodulating means. Digital filter processing means for removing a signal in a desired channel band from the signal after phase detection, a delay unit for generating the same processing delay time as the digital filter processing means, and an output signal of the digital filter processing means, An FM demodulator comprising: a synthesizing unit that synthesizes a signal subjected to delay processing by the delay unit in reverse phase; and a differentiator that extracts a frequency modulation component from the signal synthesized by the synthesizing unit.   The demodulating means includes a band pass filter for extracting a main channel component, a carrier signal generator for generating a carrier signal, a phase of a signal extracted by the band pass filter and a carrier signal from the carrier signal generator. The FM demodulator according to claim 1, further comprising a phase comparator that performs comparison and extracts a phase detection signal.   3. The FM demodulator according to claim 1, wherein the digital filter processing means is a FIR (Finite Impulse Response) type high-pass filter or band rejection filter.   A satellite-mounted command receiver comprising the FM demodulator according to any one of claims 1 to 3.

Images